Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
During a refueling event, fuel vapor located in the fuel tank may be diverted to the fuel vapor canister by opening as fuel tank isolation valve prior to the addition of fuel to the fuel tank. Fuel vapors generated during refueling may also be diverted to the fuel vapor canister in this way. Air that is stripped of fuel vapor may be diverted from the fuel vapor canister to atmosphere via a vent line, which may include a vent valve, air filter, etc.
However, restrictions, such as blockages or stuck valves may impede the movement of fuel vapor or air through the evaporative emissions system. In some scenarios, the restrictions may result in the premature termination of a refueling event. However, as there are numerous potential restriction points within the evaporative emissions system, the cause of premature refueling shutoff is often not apparent. Indeed, the most common solution is a complete dismantling of the evaporative emissions system, which may be time consuming and expensive.
The inventors herein have recognized the above described problems, and have developed systems and methods to at least partially address these issues. In one example, a method for localizing restrictions in a fuel system during refueling, comprising: monitoring fuel tank pressure, fuel vapor canister temperature, and evaporative leak check module pressure during a refueling event; and responsive to a premature shutoff event, indicating a location of a restriction among a plurality of locations based on whether monitored pressure and temperature changes during the refueling event are greater than respective thresholds. In this way, the cause of a premature shutoff event may be diagnosed without requiring additional sensors within the fuel system.
In another example, a fuel system for a vehicle, comprising: a fuel tank for storing fuel used by a vehicle engine; one or more fuel limit vent valves coupled to the fuel tank; a grade vent valve coupled to the fuel tank; a fuel tank pressure transducer coupled to the fuel tank; a canister coupled to the fuel tank for receiving and storing fuel vapors; a fuel tank isolation valve coupled between the fuel tank and the canister; a vent line coupled between the canister and atmosphere; and a control system including executable instructions stored in non-transitory memory for: during a refueling event, monitoring a fuel tank pressure; and responsive to a premature shutoff event, indicating a restriction in the grade vent valve and/or the one or more fuel limit vent valves when a fuel tank pressure change during the refueling event is less than a first fuel tank pressure threshold. In this way, the cause of a premature shutoff event may be diagnosed without requiring the dismantling and inspection of the entire fuel system, thereby saving time, money, and resources.
In yet another example, a method for a vehicle fuel system, comprising: receiving a request for a refueling event; venting fuel vapor from a fuel tank to a fuel vapor canister by opening a fuel tank isolation valve; allowing the vehicle fuel system to equilibrate; establishing baseline values for fuel tank pressure, fuel vapor canister temperature, and evaporative leak check module pressure; monitoring values for fuel tank pressure, fuel vapor canister temperature, and evaporative leak check module pressure during the refueling event; responsive to a premature shutoff event, indicating a location of a restriction among a plurality of locations based on whether monitored pressure and temperature changes during the refueling event are greater than respective thresholds. In this way, premature shutoff events may be diagnosed based on fuel system conditions during refueling, allowing for different potential restriction points to be discerned using sensors within the fuel system.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.